Personally, there are three reasons I'd want the tech package:
1. M-button - I think the ability to configure the car is one of the selling points of the new M3
2. iPod/USB interface - I think having the screen makes using any ipod/USB stored music a lot easier
3. Resale - I think those cars with Nav are going to either command a higher resale price or sell easier, either is useful when you want your next M3.
Nav isn't the highlight for me, it's all the other stuff that comes with the tech package. Also when you add up the individual components it's quite a bargain - Nav is normally $2100, EDC is $1000, Comfort access $500, so that's $3600 worth of options for $3250 plus the M-button which you can't get separately.